In offshore hydrocarbon production, there is typically a structure either a vessel such as a floating production storage and offloading (FPSO) vessel or a platform, at the surface of the sea positioned above a production field on the sea floor. There are typically several wellheads that are producing hydrocarbons to be conveyed to the vessel. Moreover, there is often other subsea equipment that requires electrical power to control, regulate, pre-treat, and/or monitor the hydrocarbon production. For example, such equipment can include, but not be limited to, a subsea pump, a subsea compressor, a control or distribution module, a lower marine riser package and blow-out preventer, an electrically submersible pump, a subsea separator, or various types of sensors and communication devices.
In order to provide such electrical power to the subsea equipment, a power umbilical extends from the structure at the surface of the sea to the field. The power umbilical typically registers with a stab or hub which receives the electrical power and distributes the electrical power through a plurality of control lines to each of the subsea equipment requiring such power.
Typically, the power umbilical utilizes copper cables as the conductor for conveying such electrical power from the vessel or structure at the surface of the sea to the subsea equipment. It has been observed that for deepwater (more than about 1500 feet depth) and ultra-deepwater (more than about 4000 feet depth), the weight of the copper itself causes deformation in an elongated manner or “creep” to occur to the copper. Such deformation or creep can ultimately lead to mechanical failure because the copper can become stretched and embrittled. However, even before such mechanical failure such deformation or creep creates losses with the electrical power being transmitted at the hangoff of the structure at the surface of the sea to the subsea equipment. For example, the creep can cause power losses or heat which can be disruptive to the subsea equipment—such as motors for the subsea pumps, electrically submersible pumps, and compressors. Generally speaking, wave disruption of electrical wave is a function of the distance or length the electrical power is being communicated or transmitted (e.g., the length of the conductor) and the magneticity of the materials adjacent the conductor. For small distances, any disruptions due to the magnetic properties of materials around or near the conductor are typically minimal. However, as the distance increases, such disruptions become larger and create a challenge because of the disruptions to the wave form of the electrical current.
Another problem that has been recognized with prior assemblies is hydrogen migration. For example, such hydrogen formation can occur when there are components comprising zinc within the umbilical. If hydrogen forms within the umbilical, then the hydrogen will try to find a path of least resistance to exit the umbilical. Sometimes the hydrogen is able to find a way through the outer jacket of the umbilical. However, it has also been observed that the hydrogen seeps through the insulators, which can prevent the water from seeping through to the conductors but not the smaller hydrogen molecules, and the hydrogen follows the conductor cables toward the ends of the umbilical. At the ends of the umbilical, the hydrogen typically becomes backed-up and begins to build pressure. When such occurrence is unknown to the operator, the high pressure hydrogen has been known to blow connection the end of the umbilical with an explosion. To prevent such explosions, operators are having to monitor hydrogen migration along the conductor cables, as well as relieving pressure when it reaches a predetermined amount.